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docbredox3 updated April 17th 2008 |
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GCE-AS-A2-IB Advanced Level Theoretical-Physical Chemistry Revision REDOX CHEMISTRY 3 Sections 8-10 Oxidation and reduction reactions in Organic Chemistry
REDOX section-index: 1. Basic redox definitions * 2. Introducing oxidation state (with sub-index) * 3. Oxidation state rules-guidelines & inorganic examples * 4. Naming inorganic compounds * 5. Using oxidation states to describe redox changes in a given inorganic reaction equation (with sub-index) * 6. Constructing full inorganic redox equations from half-equations (with sub-index) * 7. Redox titrations * 8. Organic synthesis reductions (with summary table) * 9. Organic synthesis oxidations (with summary table) * 10. Other Organic Redox Reactions (with sub-index) * 11. Carbon's ox. state in selected organic compounds * You are advised to study sections 1. to 6. in strict order and covers the requirements of AS-A2 * See also Equilibria Part 7 Redox Reactions for Half cell equilibria, electrode potential, standard hydrogen electrode, Simple cells and notation, Electrochemical Series, EØcell for reaction feasibility, 'batteries' and fuel cell systems etc. * EMAIL query?comment |
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A summary of some redox reactions used in organic synthesis is given below. Further details for selected reactions are given below the summary tables. Most of the reactions described are found in one or other of UK based GCE-AS-A2 or IB courses. The application of oxidation states to organic molecules can be tricky, but, (i) use of half-cell equations usually gets round the problem, and (ii) hopefully the oxidation state exemplars in the last section will help illuminate the situation if you are interested, but this knowledge is not required at this level? |
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8.
Summary of some ORGANIC SYNTHESIS REDUCTION REACTIONS Guide notes:
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| homologous series change on reduction | molecular structure change | (a) NaBH4 in water (lab method) | (b) LiAlH4 in e.g. ether (lab method) | (c) reflux with Sn/conc. HCl(aq) (lab method) | (d) Ni/H2 at 150oC (industry) Pd and Pt are also used as catalysts |
| 8.1 alkene ==> alkane | >C=C< ==> -CH-CH- | NO | NO | NO | YES, used |
| 8.2 aldehyde/ketone ==> primary/secondary alcohol | RCHO ==> RCH2OH and R2C=O ==> R2CHOH | YES | YES | can be reduced with Na/C2H5OH or Zn/CH3COOH mixtures | YES, used? |
| 8.3 carboxylic acid ==> primary aliphatic alcohol | RCOOH ==> RCH2OH | NO | YES | NO | YES, used? |
| 8.4 nitrile ==> primary aliphatic amine | RC |
NO | YES | NO | YES, used? |
| 8.5 nitro-aromatic ==> primary aromatic amine | e.g. C6H5NO2 ==> C6H5NH2 | NO | YES | YES | YES |
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9. Summary of some ORGANIC SYNTHESIS OXIDATION REACTIONS Guide notes
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| homologous series change on oxidation | molecular structure change | (a) heat with mod conc. H2SO4 and K2Cr2O7(aq) (lab method) | (b) reflux with KMnO4/NaOH(aq) (lab method) | (c) oxygen + catalyst or thermal decomposition (industrial methods) |
| 9.1 primary alcohol ==> aldehyde ==> carboxylic acid | RCH2OH ==> RCHO ==> RCOOH | YES | YES but only get RCOOH and of little synthetic use | e.g. CH3CH2OH ==> CH3CHO (Cu/500oC) |
| 9.2 secondary alcohol ==> ketone | R2CHOH ==> R2C=O | YES | YES but of little synthetic use | (CH3)2CHOH ==> (CH3)2C=O (Cu/500oC) |
| 9.3 tertiary alcohol ==> ? | R3C-OH fairly stable (if oxidised C-C bonds broken ==> lower RCOOH, CO2, H2O) | not readily oxidised - no synthetic use | not readily oxidised - no synthetic use | not readily oxidised - no synthetic use |
| 9.4 alkyl groups on benzene ring | e.g. C6H5CH3 ==> C6H5COOH | YES | YES | YES air/150oC/Co salt |
| 9.5 alkene ==> ? | details in appropriate box | NO | ethene ==> ethane-1,2-diol (at room temp.) | e.g. ethene ==> epoxyethane (Ag/250oC) |
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Some further details of the organic oxidations tabulated above
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10. Other miscellaneous Organic Redox Reactions This is a 'collection' of reactions not dealt with in sections 8. and 9. They may/may not be useful reactions. Section 10. reaction sub-index: 10.1 Cannizzaro reaction * 10.2 aldehydes/ketones tests * 10.3 Combustion * 10.4 Fuel cells
11. Oxidation state and organic compounds Usually the oxidation state of hydrogen is +1, and oxygen -2 in organic compounds. On this basis you can achieve a useful oxidation number analysis of simple organic compounds in an oxidation sequence. e.g. the oxidation sequence below, with the oxidation state of carbon in () and in hydrogen in (). CH4 (-4) == ox'n ==> CH3OH (-2) == ox'n ==> HCHO (0) == ox'n ==> HCOOH (+2) ==> CO2 (+4) CH3CH3 (-3,-3) = ox'n => CH3CH2OH (-3,-1) = ox'n => CH3CHO (-3,+1) = ox'n => CH3COOH (-3,+3) Note the rise of carbon's oxidation state in increments of 2, see oxidation equations for acidified potassium dichromate(VI) reaction with alcohols and aldehydes in section 9.1(a) where the half-cell oxidation equations involve a 2 electron loss from the organic molecule. Other organic molecules and redox sequences can be similarly 'analysed' ethene H2C=CH2 (-2,-2) + H2 (0) == reduction/Ni ==> ethane CH3-CH3 (-3,-3), (+1) propene CH3-CH=CH2 (-3,-1,-2) + H2 == reduction/Ni ==> CH3-CH2-CH3 (-3,-2,-3) ethanol CH3-CH2-OH (-3,-1) == ox'n ==> ethanal CH3CHO (-3,+1) == ox'n ==> CH3COOH (-3,+3) Revision notes for studying revising tutoring teaching Advanced Level GCE AS A2 CHEMISTRY courses in unofficial support the Chemistry in any advanced-subsidiary AQA, Edexcel, OCR, CIE, WJEC, SQA and CCEA (NI) UK or Cambridge/London/Edexcel International and OCR/CIE and International Baccalaureate (IB) examinations. GCE advanced-A2-AS-subsidiary-IB level chemistry examinations * GCE advanced-A2--AS-subsidiary-IB level chemistry examinations * GCE advanced-A2--AS-subsidiary-IB level chemistry examinations SITE PURPOSE EDUCATION - online learning or 'self-private-tuition' using revision notes, quizzes, practice tests involving ADVANCED LEVEL CHEMISTRY in the areas of REVISING only the CHEMISTRY at Doc Brown's Chemistry Clinic via HOMEPAGE in secondary school/schools, 6th form college/colleges, academy/academies or home self-study and may help with 1st year undergraduate university chemistry courses. Hopefully it will encourage interest and understanding of Chemistry, Earth Science and Radioactivity in any country of the world, though the site is written entirely in English. The website is designed to help and unofficially support students/teachers revise-learn/teach the chemistry for modular or co-ordinated examination science courses from UK QCA based AQA, OCR (Oxford and Cambridge), Nuffield, Salters, Cambridge International (CIE), London International, WJEC, CCEA etc. Also, national award assessments-examinations for BTEC-NVQ applied, additional and chemistry science courses, Advanced Subsidiary Level GCE-AS-A2-IB-KS5-BTEC-NVQ exams. National Chemistry assessment levels, International Baccalaureate, K12 higher US grade level examinations for the national curriculum for secondary schools and colleges. The notes should also provide some background theory for a coursework assignment or project. BUT please note that my on-line revision notes and quizzes are no substitute for good classroom teaching-lecturing and thorough studying of your own notes and textbooks, practicing past papers and a copy of the syllabus which are readily downloaded from the examination board sites, but I hope here and there they will lend a tutoring hand on some topic, unit, module etc. For final revision you have to be intellectually honest about what you don't know or follow, YOU have to take the stuff to pieces, analyse what you do/do not understand and reconstruct it so it all makes sense in the end. There is no other way, there are no magic secrets on how to revise and learn, its mainly down to hard work and just good old fashioned study and employing teach-yourself strategies without the need for extra tutors and tutoring lessons. I also think there is too much hit and miss revision using past papers (which I do NOT supply) and not enough systematic revision. I also hope it will help teachers in planning lessons and developing schemes of work for science-chemistry. There are no lesson plans on the site but there are plenty of quizzes to incorporate into classroom activities whether photocopied or on electronic whiteboard projector for use as self-tuition-assessment purposes and a variety of teaching and learning styles and the images may be used in Microsoft Word documents and powerpoint projections. The site seems to be used by a large number of home study tutors, particularly the revision notes. An individual tutor may print out the notes for science-chemistry learning teaching-tuition purposes and for background material for assignments and projects. I have no interest or time in producing WORD.doc or xxxx.pdf files of the notes at the moment. Neither have I time to write up many practical laboratory experiments ('lab'-'labs') at the moment, but the notes contain lots of background information of chemical reactions in terms of observations-balanced equations-reactants-products-theory etc. I also find it difficult to recommend specific exam websites or syllabus textbooks, it depends exactly on what you need, what you have time for, and there are so many of them to choose from and I do not supply past examination papers for classes. The sites resources include revision notes, quizzes and worksheets which provide support for home study or tuition for homework and coursework help e.g. science investigations for any of the key stage courses indicated, but I do not supply lesson plans. Dr W P Brown GCE A AS A2 IB Advanced-Subsidiary Level Chemistry 10-10-2007 GCE advanced-A2--AS-subsidiary-IB level chemistry examinations * GCE advanced-A2--AS-subsidiary-IB level chemistry examinations * GCE advanced-A2--AS-subsidiary-IB level chemistry examinations
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docbredox3 updated April 17th 2008 |